Slurry and polishing method

ABSTRACT

A slurry containing abrasive grains and a liquid medium, in which the abrasive grains include first particles and second particles in contact with the first particles, the second particles contain at least one metal compound selected from the group consisting of a metal oxide and a metal hydroxide, the metal compound contains a metal capable of taking a plurality of valences, and a ratio of the lowest valence among the plurality of valences of the metal is 0.10 or more in X-ray photoelectron spectroscopy.

TECHNICAL FIELD

The present invention relates to a slurry and a polishing method.

BACKGROUND ART

In the manufacturing steps for semiconductor elements of recent years,the importance of processing technologies for density increase andmicronization is increasing more and more. CMP (Chemical mechanicalpolishing) technology, which is one of the processing technologies, hasbecome an essential technology for the formation of a shallow trenchisolation (hereinafter, referred to as “STI”), flattening of a pre-metalinsulating material or an interlayer insulating material, formation of aplug or an embedded metal wiring, and the like in the manufacturingsteps for semiconductor elements.

Regarding polishing liquids that are most commonly used, for example,silica-based polishing liquids containing silica (silicon oxide)particles such as fumed silica and colloidal silica as abrasive grainsare mentioned. Silica-based polishing liquids have a feature of highflexibility of use, and by appropriately selecting the content ofabrasive grains, pH, additives, and the like, polishing of a widevariety of materials can be achieved regardless of whether the materialis an insulating material or an electroconductive material.

Meanwhile, as a polishing liquid mainly used for insulating materialssuch as silicon oxide, a demand for a polishing liquid containing ceriumcompound particles as abrasive grains is also increasing. For example, acerium oxide-based polishing liquid containing cerium oxide particles asabrasive grains can polish silicon oxide at a high rate even when theabrasive grain content is lower than that in the silica-based polishingliquid (for example, see Patent Literatures 1 and 2 described below).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.H10-106994

Patent Literature 2: Japanese Unexamined Patent Publication No.H08-022970

SUMMARY OF INVENTION Technical Problem

Incidentally, in recent years, 3D-NAND devices in which the cellportions of a device are laminated in the longitudinal direction havecome to the fore. In the present technology, the level differences ofthe insulating materials during cell formation are several times highercompared to the conventional planar types. According to this, in orderto maintain the throughput of the device production, it is necessary torapidly resolve the high level differences as described above in a CMPstep or the like, and it is necessary to improve the polishing rate foran insulating material.

The present invention is directed to solve the problems described above,and an object of the present invention is to provide a slurry capable ofimproving the polishing rate for an insulating material, and a polishingmethod using the slurry.

Solution to Problem

A slurry of an aspect of the present invention contains abrasive grainsand a liquid medium, in which the abrasive grains include firstparticles and second particles in contact with the first particles, thesecond particles contain at least one metal compound selected from thegroup consisting of a metal oxide and a metal hydroxide, the metalcompound contains a metal capable of taking a plurality of valences, anda ratio of the lowest valence among the plurality of valences of themetal is 0.10 or more in X-ray photoelectron spectroscopy.

According to the slurry of an aspect of the present invention, it ispossible to improve the polishing rate for an insulating material, andtherefore, an insulating material can be polished at a high polishingrate.

A polishing method of another aspect of the present invention includes astep of polishing a surface to be polished by using the above-describedslurry. According to such a polishing method, the above-describedeffects similar to those obtainable with the above-described slurry canbe obtained by using the above-described slurry.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a slurrycapable of improving the polishing rate for an insulating material and apolishing method using the slurry.

According to the present invention, it is possible to provide use of aslurry in polishing of a surface to be polished containing an insulatingmaterial. According to the present invention, it is possible to provideuse of a slurry in a flattening step of a base substrate surface that isthe manufacturing technology of semiconductor elements. According to thepresent invention, it is possible to provide use of a slurry for aflattening step of an STI insulating material, a pre-metal insulatingmaterial, or an interlayer insulating material.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail. However, the present invention is not limited to the followingembodiments.

Definition

In the present specification, a numerical range that has been indicatedby use of “to” indicates the range that includes the numerical valueswhich are described before and after “to”, as the minimum value and themaximum value, respectively. In the numerical ranges that are describedstepwise in the present specification, the upper limit value or thelower limit value of the numerical range of a certain stage can bearbitrarily combined with the upper limit value or the lower limit valueof the numerical range of another stage. In the numerical ranges thatare described in the present specification, the upper limit value or thelower limit value of the numerical value range may be replaced with thevalue shown in the examples. “A or B” may include either one of A and B,and may also include both of A and B. Materials listed as examples inthe present specification can be used singly or in combinations of twoor more, unless otherwise specifically indicated. In the presentspecification, when a plurality of substances corresponding to eachcomponent exist in the composition, the content of each component in thecomposition means the total amount of the plurality of substances thatexist in the composition, unless otherwise specified. The term “step”includes not only an independent step but also a step by which anintended action of the step is achieved, though the step cannot beclearly distinguished from other steps.

As described later, a slurry of the present embodiment contains abrasivegrains. The abrasive grains are also referred to as “abrasiveparticles”; however, in the present specification, the term “abrasivegrains” is used. Abrasive grains are generally solid particles, and itis considered that at the time of polishing, an object to be removed isremoved by the mechanical action (physical action) of the abrasivegrains and the chemical action of the abrasive grains (mainly thesurface of the abrasive grains); however, it is not limited to this. Thepolishing rate in the case of using the slurry of the present embodimentcan be compared, for example, on the basis of a polishing rate obtainedwhen the content of the abrasive grains (the total amount of particles)is adjusted to 0.1% by mass on the basis of the total mass of theslurry.

In the present specification, the term “polishing liquid” (abrasive) isdefined as a composition to be brought into contact with a surface to bepolished, at the time of polishing. The term “polishing liquid” itselfdoes not at all limit the components that are contained in the polishingliquid.

The weight average molecular weight in the present specification can bemeasured, for example, by a gel permeation chromatography method (GPC)under the following conditions using a calibration curve of standardpolystyrene.

Instrument used: Hitachi L-6000 Model [manufactured by Hitachi, Ltd.]

Column: Gel-Pak GL-R420+Gel-Pak GL-R430+Gel-Pak GL-R440 [manufactured byHitachi Chemical Co., Ltd., trade names, three columns in total]

Eluent: tetrahydrofuran

Measurement temperature: 40° C.

Flow rate: 1.75 mL/min Detector: L-3300RI [manufactured by Hitachi,Ltd.]

Slurry

The slurry of the present embodiment contains abrasive grains and aliquid medium as essential components. The slurry of the presentembodiment can be used as, for example, a polishing liquid (CMPpolishing liquid).

The abrasive grains include composite particles including firstparticles and second particles in contact with the first particles. Thesecond particles contain at least one metal compound selected from thegroup consisting of a metal oxide and a metal hydroxide, and the metalcompound contains a metal capable of taking a plurality of valences(atomic valence). Furthermore, a ratio of the lowest valence among theplurality of valences of the metal is 0.10 or more in X-rayphotoelectron spectroscopy (XPS).

The polishing rate for an insulating material (for example, siliconoxide) can be improved by using the slurry of the present embodiment.The reasons why the polishing rate for an insulating material isimproved in this way are, for example, the reasons to be as followswhile using silicon oxide as an example. However, the reasons are notlimited to the reasons to be as follows.

That is, upon polishing of silicon oxide, a first stage in which themetal atom in the abrasive grains and the silicon atom of silicon oxideare bonded via the oxygen atom (for example, a stage in which a Ce—O—Sibond is generated in a case where the metal atom is cerium) and a secondstage in which the bonding between the silicon atom and another oxygenatom in a surface to be polished is cleaved while maintaining thebonding of the metal atom-the oxygen atom-the silicon atom, to therebyremove the silicon atom from the surface to be polished are created.Further, when the abrasive grains are brought into contact with siliconoxide, the first stage is easy to proceed as the ratio of the lowestvalence among the valences of the metal in the abrasive grains islarger, and thus polishing of silicon oxide is easy to proceed on thewhole. From such a viewpoint, in a case where the ratio of the lowestvalence among the plurality of valences of the metal contained in theabrasive grains is the predetermined value or more, the first stage iseasy to proceed, and thus polishing of silicon oxide is easy to proceedon the whole. As described above, the polishing rate for silicon oxideis improved.

(Abrasive Grains)

As described above, the abrasive grains of the slurry of the presentembodiment include composite particles including first particles andsecond particles in contact with the first particles. The secondparticles contain at least one metal compound selected from the groupconsisting of a metal oxide and a metal hydroxide, and the metalcompound contains a metal (hereinafter, referred to as “metal M”)capable of taking a plurality of valences. That is, the second particlescontain at least one selected from the group consisting of an oxidecontaining the metal M and a hydroxide containing the metal M.

In the slurry of the present embodiment, the ratio of the lowest valenceamong the plurality of valences of the metal M is 0.10 or more in X-rayphotoelectron spectroscopy, from the viewpoint that the polishing ratefor an insulating material is improved. The ratio of the valence is theratio in a case where the entire amount (entire atom) of the metal M isregarded as 1, and is the ratio (unit: at %) of the number of atomshaving a target valence. The ratio of the valence can be measured by amethod described in Examples. A peak position in an X-ray photoelectronspectroscopic spectrum varies depending on the valence due to a chemicalshift. Meanwhile, the number of atoms of each peak is proportional tothe area of the peak. Therefore, a ratio between the numbers of atomshaving respective valences is obtained on the basis of the shape of thespectrum. As a method of adjusting the valence of the metal M, a methodof subjecting abrasive grains to an oxidation treatment or a reductiontreatment, and the like are exemplified. Examples of an oxidationtreatment method include a method of treating abrasive grains with areagent having oxidation action; and a method of performing ahigh-temperature treatment in air or under an oxygen atmosphere.Examples of a reduction treatment method include a method of treatingabrasive grains with a reagent having reduction action; and a method ofperforming a high-temperature treatment under a reducing atmosphere suchas hydrogen. The metal M may have a plurality of valences. The lowestvalence may be, for example, trivalent.

The ratio of the valence is preferably 0.12 or more, more preferably0.14 or more, further preferably 0.15 or more, and particularlypreferably 0.16 or more, from the viewpoint that the polishing rate foran insulating material is further improved. The ratio of the valence ispreferably 0.50 or less from the viewpoint that the polishing rate foran insulating material is further improved.

The particle size of the second particles is preferably smaller than theparticle size of the first particles. The magnitude relationship inparticle size between the first particles and the second particles canbe determined from SEM images of the composite particles, or the like.In general, particles having a small particle size have a larger surfacearea per unit mass than that of particles having a large particle size,and thus have higher reaction activity. On the other hand, themechanical action (mechanical polishing force) of particles having asmall particle size is smaller than that of particles having a largeparticle size. However, in the present embodiment, even in a case wherethe particle size of the second particles is smaller than the particlesize of the first particles, the synergetic effect of the firstparticles and the second particles can be expressed and both ofexcellent reaction activity and excellent mechanical action can beeasily achieved.

The lower limit of the particle size of the first particles ispreferably 15 nm or more, more preferably 25 nm or more, furtherpreferably 35 nm or more, particularly preferably 40 nm or more,extremely preferably 50 nm or more, highly preferably 80 nm or more, andeven more preferably 100 nm or more, from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the particle size of the first particles is preferably 1000 nmor less, more preferably 800 nm or less, further preferably 600 nm orless, particularly preferably 400 nm or less, extremely preferably 300nm or less, highly preferably 200 nm or less, and even more preferably150 nm or less, from the viewpoint of improving the dispersibility ofthe abrasive grains and the viewpoint of easily suppressing scratches ata polished surface. From the above-described viewpoints, the particlesize of the first particles is more preferably 15 to 1000 nm. Theaverage particle size (average secondary particle size) of the firstparticles may be in the above ranges.

The lower limit of the particle size of the second particles ispreferably 1 nm or more, more preferably 2 nm or more, and furtherpreferably 3 nm or more, from the viewpoint that the polishing rate foran insulating material is further improved. The upper limit of theparticle size of the second particles is preferably 50 nm or less, morepreferably 30 nm or less, further preferably 25 nm or less, particularlypreferably 20 nm or less, extremely preferably 15 nm or less, and highlypreferably 10 nm or less, from the viewpoint of improving thedispersibility of the abrasive grains and the viewpoint of easilysuppressing scratches at a polished surface. From the above-describedviewpoints, the particle size of the second particles is more preferably1 to 50 nm. The average particle size (average secondary particle size)of the second particles may be in the above ranges.

The average particle size (average secondary particle size) of theabrasive grains (the entire abrasive grains including compositeparticles and free particles) in the slurry is preferably in thefollowing range. The lower limit of the average particle size of theabrasive grains is preferably 16 nm or more, more preferably 20 nm ormore, further preferably 30 nm or more, particularly preferably 40 nm ormore, extremely preferably 50 nm or more, highly preferably 100 nm ormore, even more preferably 120 nm or more, and further preferably 140 nmor more, from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The upper limit of the average particlesize of the abrasive grains is preferably 1050 nm or less, morepreferably 1000 nm or less, further preferably 800 nm or less,particularly preferably 600 nm or less, extremely preferably 500 nm orless, highly preferably 400 nm or less, even more preferably 300 nm orless, further preferably 200 nm or less, particularly preferably 160 nmor less, and extremely preferably 155 nm or less, from the viewpoint ofimproving the dispersibility of the abrasive grains and the viewpoint ofeasily suppressing scratches at a polished surface. From theabove-described viewpoints, the average particle size of the abrasivegrains is more preferably 16 to 1050 nm.

The average particle size can be measured, for example, using a lightdiffraction scattering type particle size distribution meter (forexample, trade name: N5 manufactured by Beckman Coulter, Inc. or tradename: MICROTRAC MT3300EXII manufactured by MicrotracBEL Corp.).

The zeta potential of the abrasive grains (the zeta potential of theentire abrasive grains) in the slurry is preferably in the followingrange. The zeta potential of the abrasive grains is preferably +10 mV ormore, more preferably +20 mV or more, further preferably +25 mV or more,particularly preferably +30 mV or more, extremely preferably +40 mV ormore, and highly preferably +50 mV or more, from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the zeta potential of the abrasive grains is not particularlylimited, and is, for example, +200 mV or less.

The first particles can have a negative zeta potential. The secondparticles can have a positive zeta potential.

The zeta potential represents the surface potential of a particle. Thezeta potential can be measured, for example, using a dynamic lightscattering type zeta potential measuring apparatus (for example, tradename: DelsaNano C manufactured by Beckman Coulter, Inc.). The zetapotential of the particles can be adjusted using an additive. Forexample, by bringing monocarboxylic acid (for example, acetic acid) intocontact with particles containing cerium oxide, particles having apositive zeta potential can be obtained. Furthermore, by bringingammonium dihydrogen phosphate, a material having carboxyl group (forexample, polyacrylic acid) or the like into contact with particlescontaining cerium oxide, particles having a negative zeta potential canbe obtained.

The first particles preferably contain at least one metal (hereinafter,referred to as “metal m”) selected from the group consisting of silicon(Si), vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),copper (Cu), silver (Ag), indium (In), tin (Sn), a rare earth element(rare earth metal element), tungsten (W), and bismuth (Bi), from theviewpoint that the polishing rate for an insulating material is furtherimproved. The metal m preferably contains at least one selected from thegroup consisting of scandium (Sc) and lanthanoid as a rare earthelement, from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The metal m preferably contains at leastone selected from the group consisting of cerium (Ce), praseodymium(Pr), europium (Eu), terbium (Tb), and ytterbium (Yb) as lanthanoid,from the viewpoint that the polishing rate for an insulating material isfurther improved. The metal m preferably contains a rare earth element,more preferably contains lanthanoid, and further preferably containscerium, from the viewpoint that the polishing rate for an insulatingmaterial is further improved.

The first particles may contain an organic compound and may contain apolymer compound (polymer). Examples of the polymer compound includepolystyrene, polyphenylene sulfide, polyamide imide, an epoxy resin,polyvinylidene fluoride, polyethylene terephthalate, polybutylenetelephthalate, polyester, polyethersulfone, polylactic acid, anethylcellulose resin, and an acrylic resin.

The metal M of the second particles preferably contains a rare-earthmetal, more preferably contains lanthanoid, and further preferablycontains cerium, from the viewpoint that the polishing rate for aninsulating material is further improved. As lanthanoid, at least oneselected from the group consisting of cerium, praseodymium, europium,terbium, ytterbium, and lutetium can be used.

The second particles preferably contain a metal hydroxide and morepreferably contain a hydroxide containing cerium (cerium hydroxide),from the viewpoint that the polishing rate for an insulating material isfurther improved. The abrasive grains containing cerium hydroxide havehigher reactivity (chemical action) with an insulating material (forexample, silicon oxide) by the action of the hydroxyl group thanparticles composed of silica, cerium oxide, or the like, and aninsulating material can be polished at a higher polishing rate. Thecerium hydroxide is, for example, a compound containing a cerium ion andat least one hydroxide ion (OH⁻). The cerium hydroxide may contain ananion (for example, nitrate ion NO₃ ⁻ and sulfate ion SO₄ ²⁻) other thana hydroxide ion. For example, the cerium hydroxide may contain an anion(for example, nitrate ion NO₃ ⁻ and sulfate ion SO₄ ²⁻) bonded to acerium ion.

The cerium hydroxide can be prepared by reacting a cerium salt with analkali source (base). The cerium hydroxide can be prepared by mixing acerium salt with an alkali liquid (for example, alkali aqueoussolution). The cerium hydroxide can be obtained by mixing a cerium saltsolution (for example, a cerium salt aqueous solution) with alkaliliquid. Examples of the cerium salt include Ce(NO₃)₄, Ce(SO₄)₂,Ce(NH₄)₂(NO₃)₆, and Ce(NH₄)₄(SO₄)₄.

It is considered that particles including Ce(OH)_(a)X_(b) (in theformula, a+b×c=4) composed of cerium ion, one to three hydroxide ions(OH), and one to three anions (X^(c−)) are generated (incidentally, suchparticles are also “cerium hydroxide”) depending on productionconditions of cerium hydroxide and the like. It is considered that, inCe(OH)_(a)X_(b), an electron-withdrawing anion (X^(c−)) acts to enhancereactivity of the hydroxide ion and the polishing rate is improved withthe increase in abundance of Ce(OH)_(a)X_(b). Examples of the anions(X^(c−)) include NO₃ ⁻ and SO₄ ²⁻. It is considered that the particlescontaining cerium hydroxide can contain not only Ce(OH)_(a)X_(b) butalso Ce(OH)₄, CeO₂, or the like.

The containing of Ce(OH)_(a)X_(b) in the particles containing ceriumhydroxide can be confirmed by a method for detecting a peakcorresponding to the anions (X^(c−)) with FT-IR ATR method (Fouriertransform Infra Red Spectrometer Attenuated Total Reflection method)after washing the particles with pure water well. The existence of theanions (X^(c−)) can also be confirmed by X-ray photoelectronspectroscopy.

The abrasive grains of the slurry of the present embodiment arepreferably an embodiment in which the particle size of the secondparticles is smaller than the particle size of the first particles, thefirst particles contain cerium oxide, and the second particles containat least one cerium compound selected from the group consisting ofcerium oxide and cerium hydroxide, from the viewpoint that the polishingrate for an insulating material is further improved. The reasons why thepolishing rate for an insulating material is improved in this way are,for example, the reasons to be as follows. However, the reasons are notlimited to the reasons to be as follows.

That is, the first particles containing cerium oxide and having a largerparticle size than that of the second particles have strong mechanicalaction (mechanical property) with respect to an insulating material ascompared to the second particles. On the other hand, the secondparticles containing a cerium compound and having a smaller particlesize than that of the first particles have small mechanical action withrespect to an insulating material as compared to the first particles,but have strong chemical action (chemical property) with respect to aninsulating material since the specific surface area (surface area perunit mass) in the whole particle is large. Therefore, a synergeticeffect of improving the polishing rate is easily obtained by using thefirst particles having strong mechanical action and the second particleshaving strong chemical action.

The composite particles including the first particles and the secondparticles can be obtained by bringing the first particles and the secondparticles into contact with each other using a homogenizer, a nanomizer,a ball mill, a bead mill, a sonicator, or the like; by bringing thefirst particles and the second particles each having opposing charges toeach other into contact with each other; by bringing the first particlesand the second particles into contact with each other in a state of asmall content of the particles; or the like.

The lower limit of the content of cerium oxide in the first particles ispreferably 50% by mass or more, more preferably 70% by mass or more,further preferably 90% by mass or more, and particularly preferably 95%by mass or more, on the basis of the entire first particles (the entirefirst particles contained in the slurry; the same applies hereinafter),from the viewpoint that the polishing rate for an insulating material isfurther improved. The first particles may be an embodiment substantiallycomposed of cerium oxide (an embodiment in which substantially 100% bymass of the first particles are cerium oxide).

The lower limit of the content of the cerium compound in the secondparticles is preferably 50% by mass or more, more preferably 70% by massor more, further preferably 90% by mass or more, and particularlypreferably 95% by mass or more, on the basis of the entire secondparticles (the entire second particles contained in the slurry; the sameapplies hereinafter), from the viewpoint that the polishing rate for aninsulating material is further improved. The second particles may be anembodiment substantially composed of a cerium compound (an embodiment inwhich substantially 100% by mass of the second particles are a ceriumcompound).

The content of the second particles can be estimated on the basis of avalue of absorbance of equation below which is obtained by aspectrophotometer when light having a specific wavelength is transmittedthrough the slurry. That is, in a case where particles absorb lighthaving a specific wavelength, the light transmittance of a regioncontaining these particles is decreased. The light transmittance isdecreased not only by absorption of the particles but also byscattering, but in the second particles, the influence of scattering issmall Therefore, in the present embodiment, the content of the secondparticles can be estimated on the basis of a value of absorbancecalculated by equation below.

Absorbance=−LOG₁₀(Light transmittance [%]/100)

The lower limit of the content of the first particles in the abrasivegrains is preferably 50% by mass or more, more preferably more than 50%by mass, further preferably 60% by mass or more, particularly preferably70% by mass or more, extremely preferably 75% by mass or more, highlypreferably 80% by mass or more, even more preferably 85% by mass ormore, and further preferably 90% by mass or more, on the basis of theentire abrasive grains (the entire abrasive grains contained in theslurry; the same applies hereinafter), from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the content of the first particles in the abrasive grains ispreferably 95% by mass or less, more preferably 93% by mass or less, andfurther preferably 91% by mass or less, on the basis of the entireabrasive grains, from the viewpoint that the polishing rate for aninsulating material is further improved. From the above-describedviewpoints, the content of the first particles in the abrasive grains ismore preferably 50 to 95% by mass on the basis of the entire abrasivegrains.

The lower limit of the content of the second particles in the abrasivegrains is preferably 5% by mass or more, more preferably 7% by mass ormore, and further preferably 9% by mass or more, on the basis of theentire abrasive grains (the entire abrasive grains contained in theslurry), from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The upper limit of the content of thesecond particles in the abrasive grains is preferably 50% by mass orless, more preferably less than 50% by mass, further preferably 40% bymass or less, particularly preferably 30% by mass or less, extremelypreferably 20% by mass or less, and highly preferably 10% by mass orless, on the basis of the entire abrasive grains, from the viewpointthat the polishing rate for an insulating material is further improved.From the above-described viewpoints, the content of the second particlesin the abrasive grains is more preferably 5 to 50% by mass on the basisof the entire abrasive grains.

The lower limit of the content of cerium oxide in the abrasive grains ispreferably 50% by mass or more, more preferably more than 50% by mass,further preferably 60% by mass or more, particularly preferably 70% bymass or more, extremely preferably 75% by mass or more, highlypreferably 80% by mass or more, even more preferably 85% by mass ormore, and further preferably 90% by mass or more, on the basis of theentire abrasive grains (the entire abrasive grains contained in theslurry), from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The upper limit of the content of ceriumoxide in the abrasive grains is preferably 95% by mass or less, morepreferably 93% by mass or less, and further preferably 91% by mass orless, on the basis of the entire abrasive grains, from the viewpointthat the polishing rate for an insulating material is further improved.From the above-described viewpoints, the content of cerium oxide in theabrasive grains is more preferably 50 to 95% by mass on the basis of theentire abrasive grains.

The lower limit of the content of cerium hydroxide in the abrasivegrains is preferably 5% by mass or more, more preferably 7% by mass ormore, and further preferably 9% by mass or more, on the basis of theentire abrasive grains (the entire abrasive grains contained in theslurry), from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The upper limit of the content of ceriumhydroxide in the abrasive grains is preferably 50% by mass or less, morepreferably less than 50% by mass, further preferably 40% by mass orless, particularly preferably 30% by mass or less, extremely preferably20% by mass or less, and highly preferably 10% by mass or less, on thebasis of the entire abrasive grains, from the viewpoint that thepolishing rate for an insulating material is further improved. From theabove-described viewpoints, the content of cerium hydroxide in theabrasive grains is more preferably 5 to 50% by mass on the basis of theentire abrasive grains.

The lower limit of the content of the first particles is preferably 50%by mass or more, more preferably more than 50% by mass, furtherpreferably 60% by mass or more, particularly preferably 70% by mass ormore, extremely preferably 75% by mass or more, highly preferably 80% bymass or more, even more preferably 85% by mass or more, and furtherpreferably 90% by mass or more, on the basis of the total amount of thefirst particles and the second particles, from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the content of the first particles is preferably 95% by mass orless, more preferably 93% by mass or less, and further preferably 91% bymass or less, on the basis of the total amount of the first particlesand the second particles, from the viewpoint that the polishing rate foran insulating material is further improved. From the above-describedviewpoints, the content of the first particles is more preferably 50 to95% by mass on the basis of the total amount of the first particles andthe second particles.

The lower limit of the content of the second particles is preferably 5%by mass or more, more preferably 7% by mass or more, and furtherpreferably 9% by mass or more, on the basis of the total amount of thefirst particles and the second particles, from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the content of the second particles is preferably 50% by massor less, more preferably less than 50% by mass, further preferably 40%by mass or less, particularly preferably 30% by mass or less, extremelypreferably 20% by mass or less, and highly preferably 10% by mass orless, on the basis of the total amount of the first particles and thesecond particles, from the viewpoint that the polishing rate for aninsulating material is further improved. From the above-describedviewpoints, the content of the second particles is more preferably 5 to50% by mass on the basis of the total amount of the first particles andthe second particles.

The lower limit of the content of the first particles in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.05% by mass or more, extremely preferably 0.07% by mass or more, andhighly preferably 0.08% by mass or more, on the basis of the total massof the slurry, from the viewpoint that the polishing rate for aninsulating material is further improved. The upper limit of the contentof the first particles in the slurry is preferably 5% by mass or less,more preferably 3% by mass or less, further preferably 1% by mass orless, particularly preferably 0.5% by mass or less, extremely preferably0.3% by mass or less, highly preferably 0.1% by mass or less, even morepreferably 0.09% by mass or less, and further preferably 0.085% by massor less, on the basis of the total mass of the slurry, from theviewpoint that the polishing rate for an insulating material is furtherimproved and the viewpoint of enhancing the storage stability of theslurry. From the above-described viewpoints, the content of the firstparticles in the slurry is more preferably 0.005 to 5% by mass on thebasis of the total mass of the slurry.

The lower limit of the content of the second particles in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.012% by mass or more, extremely preferably 0.015% by mass or more, andhighly preferably 0.016% by mass or more, on the basis of the total massof the slurry, from the viewpoint of further enhancing a chemicalinteraction between the abrasive grains and a surface to be polished sothat the polishing rate for an insulating material is further improved.The upper limit of the content of the second particles in the slurry ispreferably 5% by mass or less, more preferably 3% by mass or less,further preferably 1% by mass or less, particularly preferably 0.5% bymass or less, extremely preferably 0.1% by mass or less, highlypreferably 0.05% by mass or less, even more preferably 0.04% by mass orless, further preferably 0.035% by mass or less, further preferably0.03% by mass or less, particularly preferably 0.02% by mass or less,and extremely preferably 0.018% by mass or less, on the basis of thetotal mass of the slurry, from the viewpoints of easily avoiding theaggregation of the abrasive grains, and easily obtaining a morefavorable chemical interaction between the abrasive grains and a surfaceto be polished to easily utilize the properties of the abrasive grainseffectively. From the above-described viewpoints, the content of thesecond particles in the slurry is more preferably 0.005 to 5% by mass onthe basis of the total mass of the slurry.

The lower limit of the content of cerium oxide in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.05% by mass or more, extremely preferably 0.07% by mass or more, andhighly preferably 0.08% by mass or more, on the basis of the total massof the slurry, from the viewpoint that the polishing rate for aninsulating material is further improved. The upper limit of the contentof cerium oxide in the slurry is preferably 5% by mass or less, morepreferably 3% by mass or less, further preferably 1% by mass or less,particularly preferably 0.5% by mass or less, extremely preferably 0.3%by mass or less, highly preferably 0.1% by mass or less, even morepreferably 0.09% by mass or less, and further preferably 0.085% by massor less, on the basis of the total mass of the slurry, from theviewpoint that the polishing rate for an insulating material is furtherimproved and the viewpoint of enhancing the storage stability of theslurry. From the above-described viewpoints, the content of cerium oxidein the slurry is more preferably 0.005 to 5% by mass on the basis of thetotal mass of the slurry.

The lower limit of the content of cerium hydroxide in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.012% by mass or more, extremely preferably 0.015% by mass or more, andhighly preferably 0.016% by mass or more, on the basis of the total massof the slurry, from the viewpoint of further enhancing a chemicalinteraction between the abrasive grains and a surface to be polished sothat the polishing rate for an insulating material is further improved.The upper limit of the content of cerium hydroxide in the slurry ispreferably 5% by mass or less, more preferably 3% by mass or less,further preferably 1% by mass or less, particularly preferably 0.5% bymass or less, extremely preferably 0.1% by mass or less, highlypreferably 0.05% by mass or less, even more preferably 0.04% by mass orless, further preferably 0.035% by mass or less, further preferably0.03% by mass or less, particularly preferably 0.02% by mass or less,and extremely preferably 0.018% by mass or less, on the basis of thetotal mass of the slurry, from the viewpoints of easily avoiding theaggregation of the abrasive grains, and easily obtaining a morefavorable chemical interaction between the abrasive grains and a surfaceto be polished to easily utilize the properties of the abrasive grainseffectively. From the above-described viewpoints, the content of ceriumhydroxide in the slurry is more preferably 0.005 to 5% by mass on thebasis of the total mass of the slurry.

The lower limit of the content of the abrasive grains in the slurry ispreferably 0.01% by mass or more, more preferably 0.05% by mass or more,further preferably 0.08% by mass or more, and particularly preferably0.1% by mass or more, on the basis of the total mass of the slurry, fromthe viewpoint that the polishing rate for an insulating material isfurther improved. The upper limit of the content of the abrasive grainsin the slurry is preferably 10% by mass or less, more preferably 5% bymass or less, further preferably 1% by mass or less, particularlypreferably 0.5% by mass or less, extremely preferably 0.1% by mass orless, highly preferably 0.2% by mass or less, even more preferably 0.15%by mass or less, further preferably 0.135% by mass or less, andparticularly preferably 0.13% by mass or less, on the basis of the totalmass of the slurry, from the viewpoint of enhancing the storagestability of the slurry. From the above-described viewpoints, thecontent of the abrasive grains in the slurry is more preferably 0.01 to10% by mass on the basis of the total mass of the slurry.

The slurry of the present embodiment may contain particles other thanthe composite particles including the first particles and the secondparticles. Examples of such other particles include the first particlesnot in contact with the second particles; the second particles not incontact with the first particles; and third particles composed ofsilica, alumina, zirconia, yttria, or the like (particles not includingthe first particles and the second particles).

(Liquid Medium)

The liquid medium is not particularly limited; however, water such asdeionized water or ultrapure water is preferred. The content of theliquid medium may be the balance of the slurry remaining after excludingthe contents of other constituent components, and the content is notparticularly limited.

(Optional Components)

The slurry of the present embodiment may further contain optionaladditives. Examples of the optional additives include a material havinga carboxyl group (excluding a compound corresponding to apolyoxyalkylene compound or a water-soluble polymer), a polyoxyalkylenecompound, a water-soluble polymer, an oxidizing agent (for example,hydrogen peroxide), and a dispersant (for example, a phosphoricacid-based inorganic salt). The respective additives can be used singlyor in combination of two or more kinds thereof.

Examples of the material having a carboxyl group include monocarboxylicacids such as acetic acid, propionic acid, butyric acid, and valericacid; hydroxy acids such as lactic acid, malic acid, and citric acid;dicarboxylic acids such as malonic acid, succinic acid, fumaric acid,and maleic acid; polycarboxylic acids such as polyacrylic acid andpolymaleic acid; and amino acids such as arginine, histidine, andlysine.

Examples of the polyoxyalkylene compound include a polyalkylene glycoland a polyoxyalkylene derivative.

Examples of the polyalkylene glycol include polyethylene glycol,polypropylene glycol, and polybutylene glycol. The polyalkylene glycolis preferably at least one selected from the group consisting ofpolyethylene glycol and polypropylene glycol, and is more preferablypolyethylene glycol.

A polyoxyalkylene derivative is, for example, a compound obtained byintroducing a functional group or a substituent to a polyalkyleneglycol, or a compound obtained by adding a polyalkylene oxide to anorganic compound. Examples of the functional group or a substituentinclude an alkyl ether group, an alkyl phenyl ether group, a phenylether group, a styrenated phenyl ether group, a glyceryl ether group, analkylamine group, a fatty acid ester group, and a glycol ester group.Examples of the polyoxyalkylene derivative include a polyoxyethylenealkyl ether, polyoxyethylene bisphenol ether (for example, manufacturedby NIPPON NYUKAZAI CO., LTD., BA GLYCOL series), polyoxyethylenestyrenated phenyl ether (for example, manufactured by Kao Corporation,EMULGEN series), a polyoxyethylene alkyl phenyl ether (for example,manufactured by DKS Co. Ltd., NOIGEN EA series), a polyoxyalkylenepolyglyceryl ether (for example, manufactured by Sakamoto Yakuhin KogyoCo., Ltd., SC-E series and SC-P series), a polyoxyethylene sorbitanfatty acid ester (for example, manufactured by DKS Co. Ltd., SORGEN TWseries), a polyoxyethylene fatty acid ester (for example, manufacturedby Kao Corporation, EMANON series), a polyoxyethylene alkylamine (forexample, manufactured by DKS Co. Ltd., AMIRADIN D), and other compoundshaving a polyalkylene oxide added thereto (for example, manufactured byNissin Chemical Co., Ltd., SURFINOL 465, and manufactured by NIPPONNYUKAZAI CO., LTD., TMP series).

The “water-soluble polymer” is defined as a polymer which is dissolvedin 100 g of water in an amount of 0.1 g or more. A polymer thatcorresponds to the polyoxyalkylene compound is not to be included in the“water-soluble polymer”. The water-soluble polymer is not particularlylimited, and examples include acrylic polymers such as polyacrylamideand polydimethylacrylamide; polysaccharides such as carboxymethylcellulose, agar, curdlan, dextrin, cyclodextrin, and pullulan;vinyl-based polymers such as polyvinyl alcohol, polyvinylpyrrolidone,and polyacrolein; glycerin-based polymers such as polyglycerin and apolyglycerin derivative; and polyethylene glycol.

(Characteristics of Slurry)

The lower limit of the pH of the slurry of the present embodiment ispreferably 2.0 or more, more preferably 2.5 or more, further preferably2.8 or more, particularly preferably 3.0 or more, extremely preferably3.2 or more, highly preferably 3.5 or more, even more preferably 4.0 ormore, and further preferably 4.1 or more, from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the pH is preferably 7.0 or less, more preferably 6.5 or less,further preferably 6.0 or less, particularly preferably 5.0 or less,extremely preferably 4.8 or less, highly preferably 4.7 or less, evenmore preferably 4.6 or less, further preferably 4.5 or less, andparticularly preferably 4.4 or less, from the viewpoint that the storagestability of the slurry is further improved. From the above-describedviewpoints, the pH is more preferably 2.0 to 7.0. The pH of the slurryis defined as the pH at a liquid temperature of 25° C.

The pH of the slurry can be adjusted by means of an acid component suchas an inorganic acid or an organic acid; an alkali component such asammonia, sodium hydroxide, tetramethylammonium hydroxide (TMAH),imidazole, or an alkanolamine; or the like. Furthermore, a bufferingagent may be added in order to stabilize the pH. Furthermore, abuffering agent may be added as a buffer solution (a liquid containing abuffering agent). Examples of such a buffer solution include an acetatebuffer solution and a phthalate buffer solution.

The pH of the slurry of the present embodiment can be measured by a pHmeter (for example, Model No. PHL-40 manufactured by DKK-TOACORPORATION). Specifically, for example, a pH meter is subjected totwo-point calibration using a phthalate pH buffer solution (pH: 4.01)and a neutral phosphate pH buffer solution (pH: 6.86) as standard buffersolutions, subsequently the electrode of the pH meter is introduced intothe slurry, and the value after being stabilized after a lapse of twominutes or longer is measured. The liquid temperatures of the standardbuffer solutions and the slurry are all set to 25° C.

In a case where the slurry of the present embodiment is used as a CMPpolishing liquid, the constituent components of the polishing liquid maybe stored as a one-pack polishing liquid, or may be stored as amulti-pack (for example, two-pack) polishing liquid set in which theconstituent components of the polishing liquid are divided into a slurryand an additive liquid such that a slurry (first liquid) containingabrasive grains and a liquid medium, and an additive liquid (secondliquid) containing additives and a liquid medium are mixed to form thepolishing liquid. The additive liquid may contain, for example, anoxidizing agent. The constituent components of the polishing liquid maybe stored as a polishing liquid set while being divided into three ormore liquids.

In the polishing liquid set, the slurry and the additive liquid aremixed immediately before polishing or during polishing to prepare thepolishing liquid. Furthermore, a one-pack polishing liquid may be storedas a stock solution for a polishing liquid with a reduced liquid mediumcontent and used by dilution with a liquid medium at the time ofpolishing. A multi-pack polishing liquid set may be stored as a stocksolution for a slurry and a stock solution for an additive liquid withreduced liquid medium contents, and used by dilution with a liquidmedium at the time of polishing.

Polishing Method

The polishing method (such as a polishing method of a base substrate) ofthe present embodiment includes a polishing step of polishing a surfaceto be polished (such as a surface to be polished of a base substrate) byusing the above-described slurry. The slurry in the polishing step maybe a polishing liquid obtained by mixing the slurry and the additiveliquid of the above-described polishing liquid set.

In the polishing step, for example, in a state where a material to bepolished of the base substrate that has the material to be polished ispressed against a polishing pad (polishing cloth) of a polishing platen,the slurry is supplied between the material to be polished and thepolishing pad, and the base substrate and the polishing platen are movedrelative to each other to polish the surface to be polished of thematerial to be polished. In the polishing step, for example, at least apart of a material to be polished is removed by polishing.

As the base substrate that is to be polished, a substrate to be polishedor the like is exemplified. As the substrate to be polished, forexample, a base substrate in which a material to be polished is formedon a substrate for semiconductor element production (for example, asemiconductor substrate in which an STI pattern, a gate pattern, awiring pattern, or the like is formed) is exemplified. Examples of thematerial to be polished include an insulating material such as siliconoxide. The material to be polished may be a single material or aplurality of materials. In a case where a plurality of materials areexposed on a surface to be polished, they can be considered as amaterial to be polished. The material to be polished may be in the formof a film (film to be polished) and may be an insulating film such as asilicon oxide film.

By polishing a material to be polished (for example, an insulatingmaterial such as silicon oxide) formed on such a substrate with theslurry and removing an excess part, it is possible to eliminateirregularities on the surface of a material to be polished and toproduce a smooth surface over the entire surface of the polishedmaterial.

In the polishing method of the present embodiment, as a polishingapparatus, it is possible to use a common polishing apparatus which hasa holder capable of holding a base substrate having a surface to bepolished and a polishing platen to which a polishing pad can be pasted.A motor or the like in which the number of rotations can be changed isattached to each of the holder and the polishing platen. As thepolishing apparatus, for example, polishing apparatus: F-REX300manufactured by EBARA CORPORATION, or polishing apparatus: MIRRAmanufactured by Applied Materials, Inc. can be used.

As the polishing pad, common unwoven cloth, a foamed body, an unfoamedbody, and the like can be used. As the material for the polishing pad,it is possible to use a resin such as polyurethane, an acrylic resin,polyester, an acrylic-ester copolymer, polytetrafluoroethylene,polypropylene, polyethylene, poly-4-methylpentene, cellulose, celluloseester, polyamide (for example, Nylon (trade name) and aramid),polyimide, polyimidamide, a polysiloxane copolymer, an oxirane compound,a phenolic resin, polystyrene, polycarbonate, or an epoxy resin.Particularly, from the viewpoint of obtaining further excellentpolishing rate and flattening properties, the material for the polishingpad is preferably at least one selected from the group consisting of afoamed polyurethane and a non-foamed polyurethane. It is preferable thatthe polishing pad is subjected to groove processing, by which the slurryaccumulates thereon.

Polishing conditions are not limited, but the upper limit of therotation speed of a polishing platen is preferably 200 min′ (min′=rpm)or less such that the base substrate is not let out, and the upper limitof the polishing pressure to be applied to the base substrate(processing load) is preferably 100 kPa or less from the viewpoint ofeasily suppressing the generation of polishing scratches. The slurry ispreferably continuously supplied to the polishing pad with a pump or thelike during polishing. There are no limitations on the supply amount forthis, however, it is preferable that the surface of the polishing pad isalways covered with the slurry.

The present embodiment is preferably used for polishing a surface to bepolished containing silicon oxide. According to the present embodiment,it is possible to provide use of a slurry in polishing of a surface tobe polished containing silicon oxide. The present embodiment can besuitably used in formation of an STI and polishing of an interlayerinsulating material at a high rate. The lower limit of the polishingrate for an insulating material (for example, silicon oxide) ispreferably 850 nm/min or more, more preferably 900 nm/min or more, andfurther preferably 1000 nm/min or more.

The present embodiment can also be used in polishing of a pre-metalinsulating material. Examples of the pre-metal insulating materialinclude silicon oxide, phosphorus-silicate glass,boron-phosphorus-silicate glass, silicon oxyfluoride, and fluorinatedamorphous carbon.

The present embodiment can also be applied to materials other than theinsulating material such as silicon oxide. Examples of such a materialinclude high permittivity materials such as Hf-based, Ti-based, andTa-based oxides; semiconductor materials such as silicon, amorphoussilicon, SiC, SiGe, Ge, GaN, GaP, GaAs, and organic semiconductors;phase-change materials such as GeSbTe; inorganic electroconductivematerials such as ITO; and polymer resin materials such aspolyimide-based, polybenzooxazole-based, acrylic, epoxy-based, andphenol-based materials.

The present embodiment can be applied not only to film-like objects tobe polished, but also to various types of substrates made of glass,silicon, SiC, SiGe, Ge, GaN, GaP, GaAs, sapphire, plastics, or the like.

The present embodiment can be used not only for the production ofsemiconductor elements, but also for the production of image displaydevices such as TFT or organic EL; optical components such as aphotomask, a lens, a prism, an optical fiber, or a single crystalscintillator; optical elements such as an optical switching element oran optical waveguide; light-emitting elements such as a solid laser or ablue laser LED; and magnetic storage devices such as a magnetic disc ora magnetic head.

EXAMPLES

Hereinafter, the present invention will be specifically described basedon Examples; however, the present invention is not limited to thefollowing Examples.

Preparation of Cerium Oxide Slurry

Particles containing cerium oxide (first particles; hereinafter,referred to as “cerium oxide particles”) and trade name; ammoniumdihydrogen phosphate manufactured by Wako Pure Chemical Industries, Ltd.(molecular weight: 97.99) were mixed to prepare a cerium oxide slurry(pH: 7) containing 5.0% by mass (solid content amount) of the ceriumoxide particles. The mixing amount of the ammonium dihydrogen phosphatewas adjusted to 1% by mass on the basis of the total amount of thecerium oxide particles.

An adequate amount of the cerium oxide slurry was introduced into tradename: MICROTRAC MT3300EXII manufactured by MicrotracBEL Corp., and theaverage particle size of the cerium oxide particles was measured. Thedisplayed average particle size value was obtained as the averageparticle size (average secondary particle size). The average particlesize of the cerium oxide particles in the cerium oxide slurry was 145nm.

An adequate amount of the cerium oxide slurry was introduced into tradename: DelsaNano C manufactured by Beckman Coulter, Inc. and measurementwas performed twice at 25° C. The average value of the displayed zetapotentials was obtained as the zeta potential. The zeta potential of thecerium oxide particles in the cerium oxide slurry was −55 mV.

Preparation of Cerium Hydroxide Slurry

(Synthesis of Cerium Hydroxide)

480 g of an aqueous 50% by mass Ce(NH₄)₂(NO₃)₆ solution (trade name:CANSO liquid manufactured by Nihon Kagaku Sangyo Co., Ltd.) was mixedwith 7450 g of pure water to obtain a solution. Next, while thissolution was stirred, 750 g of an aqueous solution of imidazole (10% bymass aqueous solution, 1.47 mol/L) was added dropwise thereto at amixing rate of 5 mL/min, and thereby a precipitate containing ceriumhydroxide was obtained. The cerium hydroxide was synthesized at atemperature of 20° C. and a stirring speed of 500 min′ The stirring wasperformed using a 3-blade pitch paddle with a total blade section lengthof 5 cm.

The obtained precipitate (precipitate containing cerium hydroxide) wassubjected to centrifugal separation (4000 min′, for 5 minutes), and thensubjected to solid-liquid separation with removal of a liquid phase bydecantation. 10 g of the particles obtained by solid-liquid separationwere mixed with 990 g of water, and then the particles were dispersed inwater using an ultrasonic cleaner, thereby preparing a cerium hydroxideslurry (content of particles: 1.0% by mass) containing particles thatcontained cerium hydroxide (second particles; hereinafter, referred toas “cerium hydroxide particles”).

(Measurement of Average Particle Size)

When the average particle size (average secondary particle size) of thecerium hydroxide particles in the cerium hydroxide slurry was measuredusing trade name: N5 manufactured by Beckman Coulter, Inc., a value of10 nm was obtained. The measuring method was as follows. First, about 1mL of a measuring sample (cerium hydroxide slurry, aqueous dispersionliquid) containing 1.0% by mass of cerium hydroxide particles wasintroduced into a 1-cm square cell, and then the cell was placed in theN5. Measurement was performed at 25° C. with the refractive index set to1.333 and the viscosity set to 0.887 mPa·s as the measuring sampleinformation of N5 software, and the value displayed as Unimodal SizeMean was read off.

(Measurement of Zeta Potential)

An adequate amount of the cerium hydroxide slurry was introduced intotrade name: DelsaNano C manufactured by Beckman Coulter, Inc. andmeasurement was performed twice at 25° C. The average value of thedisplayed zeta potentials was obtained as the zeta potential. The zetapotential of the cerium hydroxide particles in the cerium hydroxideslurry was +50 mV.

(Structural Analysis of Cerium Hydroxide Particles)

An adequate amount of the cerium hydroxide slurry was taken andvacuum-dried to isolate the cerium hydroxide particles, and thensufficiently washed with pure water to obtain a sample. When theobtained sample was measured by FT-IR ATR method, a peak based onnitrate ion (NO₃ ⁻) was observed in addition to a peak based onhydroxide ion (OH⁻). Furthermore, when the same sample was measured byXPS (N-XPS) for nitrogen, a peak based on nitrate ion was observed whileno peak based on NH₄ ⁺ was observed. These results confirmed that thecerium hydroxide particles at least partially contained particles havingnitrate ion bonded to a cerium element. Furthermore, since particleshaving hydroxide ion bonded to a cerium element were at least partiallycontained in the cerium hydroxide particles, it was confirmed that thecerium hydroxide particles contained cerium hydroxide. These resultsconfirmed that the cerium hydroxide contained a hydroxide ion bonded toa cerium element.

Preparation of Slurry Example 1

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 25 g of the cerium hydroxide slurry and 1935 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a test slurry containingcomposite particles including cerium oxide particles and ceriumhydroxide particles that were in contact with the cerium oxide particles(content of cerium oxide particles: 0.1% by mass, content of ceriumhydroxide particles: 0.0125% by mass) was prepared.

Example 2

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 30 g of the cerium hydroxide slurry and 1930 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a test slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.015%by mass) was prepared.

Example 3

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 35 g of the cerium hydroxide slurry and 1925 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a test slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.0175%by mass) was prepared.

Example 4

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 40 g of the cerium hydroxide slurry and 1920 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a test slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.02% bymass) was prepared.

Comparative Example 1

After mixing 40 g of the cerium oxide slurry and 1960 g of ion-exchangewater while stirring at a rotation speed of 300 rpm using a stirringblade of two blades, stirring was performed while being irradiated withultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a test slurry containing ceriumoxide particles (content of cerium oxide particles: 0.1% by mass) wasprepared.

Comparative Example 2

After mixing 200 g of the cerium hydroxide slurry and 1800 g ofion-exchange water while stirring at a rotation speed of 300 rpm using astirring blade of two blades, stirring was performed while beingirradiated with ultrasonic waves using an ultrasonic cleaner (devicename: US-105) manufactured by SND Co., Ltd. Thereby, a test slurrycontaining cerium hydroxide particles (content of cerium hydroxideparticles: 0.1% by mass) was prepared.

Measurement of Valence

The test slurry was treated for 30 minutes at a centrifugal accelerationof 1.1×10⁴ G by using a centrifugal separator (trade name: OptimaMAX-TL) manufactured by Beckman Coulter, Inc. so as to separate thesolid phase and the liquid phase (supernatant solution). After theliquid phase was removed, the solid phase was vacuum-dried at 25° C. for24 hours, and thereby a measurement sample was obtained. The valence ofcerium contained in the abrasive grains in this measurement sample wasmeasured by X-ray photoelectron spectroscopy.

As the measuring apparatus of the X-ray photoelectron spectroscopy(XPS), trade name “K-Alpha” manufactured by Thermo Fisher ScientificInc. was used. The measurement conditions are as follows.

[XPS Conditions]

Pass energy: 100 eV

Cumulated number: 10 times

Bonding energy: Range of 870 to 930 eV

Excited X-ray: monochromatic Al Kα1,2 radiation (1486.6 eV)

X-ray diameter: 200 μm

Photoelectron escape angle: 45°

Next, regarding the valence of cerium, a waveform due to trivalent and awaveform due to tetravalent were separated by using analysis softwaresupplied with the apparatus. The waveform separation was performedaccording to the method described in literature “Surface Science vol.563 (2004) p. 74-82”. Then, the ratio of trivalent was obtained on thebasis of formula below. The measurement results are shown in Table 1.

Ratio of trivalent=(Trivalent amount [at %]/(Trivalent amount [at%]+Tetravalent amount [at %])

Measurement of pH

The pH of the test slurry was measured using Model No. PHL-40manufactured by DKK-TOA CORPORATION. The measurement results are shownin Table 1.

Measurement of Zeta Potential of Abrasive Grains

An adequate amount of the test slurry was introduced into trade name“DelsaNano C” manufactured by Beckman Coulter, Inc. The measurement wasperformed at 25° C. twice, and the average value of the displayed zetapotentials was adopted. The measurement results are shown in Table 1.

Measurement of Average Particle Size of Abrasive Grains

Each of the test slurries of Examples 1 to 4 and Comparative Example 1was introduced in an adequate amount into trade name: MICROTRACMT3300EXII manufactured by MicrotracBEL Corp., and measurement of theaverage particle size of the abrasive grains was performed. Furthermore,the test slurry of Comparative Example 2 was introduced in an adequateamount into trade name: N5 manufactured by Beckman Coulter, Inc., andmeasurement of the average particle size of the abrasive grains wasperformed. The displayed each average particle size value was obtainedas the average particle size (average secondary particle size) of theabrasive grains. The measurement results are shown in Table 1.

Measurement of Polishing Rate

The content of the abrasive grains (the total amount of particles) inthe test slurry was adjusted to 0.1% by mass (diluted with ion-exchangewater) to prepare a CMP polishing liquid. The substrate to be polishedwas polished by using this CMP polishing liquid under the polishingconditions below. Values of the valence and the pH in the CMP polishingliquid and the zeta potential and the average particle size of theabrasive grains were the same as the values in the test slurry mentionedabove.

[CMP Polishing Conditions]

Polishing apparatus: MIRRA (manufactured by Applied Materials, Inc.)

Flow rate of CMP polishing liquid: 200 mL/min

Substrate to be polished: As a blanket wafer having no pattern formedthereon, a substrate to be polished having a silicon oxide film having athickness of 2 μm, which had been formed by a plasma CVD method, on asilicon substrate was used.

Polishing pad: Foamed polyurethane resin having closed pores(manufactured by Dow Chemical Japan Ltd., Product No.: IC1010)

Polishing pressure: 13 kPa (2.0 psi)

Rotation numbers of substrate to be polished and polishing platen:Substrate to be polished/polishing platen=93/87 rpm

Polishing time: 1 minute

Washing of wafer: After a CMP treatment, washing was performed withwater while applying an ultrasonic wave, and then drying was performedwith a spin dryer.

The polishing rate for a silicon oxide film (SiO₂RR) that had beenpolished and washed under the above-described conditions was obtained bythe formula below. The measurement results are shown in Table 1. Thefilm thickness difference of the silicon oxide film before and afterpolishing was obtained using a light interference type film thicknessmeasuring apparatus (trade name: F80 manufactured by Filmetrics Japan,Inc.).

Polishing rate (RR)=(Film thickness difference [nm] of silicon oxidefilm before and after polishing)/(Polishing time: 1 [min])

TABLE 1 Zeta Average Polishing Ratio of potential particle size ratetrivalent pH [mV] [nm] [nm/min] Example 1 0.17 3.9 55 155 360 Example 20.20 3.9 52 155 401 Example 3 0.17 4.0 52 155 450 Example 4 0.16 4.1 50155 456 Comparative 0.05 7.0 −62 145 245 Example 1 Comparative 0.04 4.050 10 28 Example 2

1. A slurry comprising abrasive grains and a liquid medium, wherein theabrasive grains include first particles and second particles in contactwith the first particles, the second particles contain at least onemetal compound selected from the group consisting of a metal oxide and ametal hydroxide, the metal compound contains a metal capable of taking aplurality of valences, and a ratio of the lowest valence among theplurality of valences of the metal is 0.10 or more in X-rayphotoelectron spectroscopy.
 2. The slurry according to claim 1, whereinthe lowest valence is trivalent.
 3. The slurry according to claim 1,wherein the metal contains a rare-earth metal.
 4. The slurry accordingto claim 1, wherein the metal contains cerium.
 5. The slurry accordingto claim 1, wherein the first particles contain at least one selectedfrom the group consisting of silicon, vanadium, manganese, iron, cobalt,nickel, copper, silver, indium, tin, a rare earth element, tungsten, andbismuth.
 6. The slurry according to claim 1, wherein the first particlescontain cerium oxide.
 7. The slurry according to claim 1, wherein a zetapotential of the abrasive grains is +10 mV or more.
 8. A polishingmethod comprising a step of polishing a surface to be polished by usingthe slurry according to claim
 1. 9. The slurry according to claim 1,wherein the first particles contain cerium oxide.
 10. The slurryaccording to claim 1, wherein the second particles contain the metalhydroxide.
 11. The slurry according to claim 9, wherein the secondparticles contain the metal hydroxide.
 12. The slurry according to claim1, wherein the second particles contain cerium hydroxide.
 13. The slurryaccording to claim 9, wherein the second particles contain ceriumhydroxide.
 14. The slurry according to claim 1, wherein a particle sizeof the second particles is smaller than a particle size of the firstparticles.
 15. The slurry according to claim 1, wherein a particle sizeof the first particles is 15 to 1000 nm.
 16. The slurry according toclaim 1, wherein a particle size of the second particles is 1 to 50 nm.17. The slurry according to claim 1, wherein a content of ceriumhydroxide in the abrasive grains is 5 to 50% by mass on the basis of theentire abrasive grains.
 18. The slurry according to claim 1, wherein acontent of the abrasive grains is 0.01 to 1% by mass on the basis of thetotal mass of the slurry.
 19. The slurry according to claim 1, whereinpH is 2.0 to 5.0.
 20. The polishing method according to claim 8, whereinthe surface to be polished contains silicon oxide.